Newly elected Green and UK Independence Party MEPs, swept into the European parliament on the back of the new PR voting system, yesterday recovered from their shock sufficiently to predict their parties could now go on to win seats at Westminster.

Both minority parties, who have nothing in common but an opposition to the euro and an air of thrilled astonishment at achieving power, insisted they had now established their electoral credibility.

The Greens, who cracked open champagne at a press conference to celebrate winning their first two seats in Strasbourg, claimed they could return MPs within seven or eight years.

Caroline Lucas, elected in London, and Jean Lambert, representing the south east region, said they owed their victory at least in part to disaffected traditional Labour supporters searching for a more radical alternative to Tony Blair.

Campaigners, who wooed thousands of viewers with a psychedelic pop video-style election broadcast, believe a pledge to call for a complete ban on genetically modified food struck a chord with voters.

UKIP, which wants a withdrawal from the European Union and opposes the PR system through which its three representatives were elected, confirmed its MEPs would take up their seats in Strasbourg. However, the party says Michael Holmes, UKIP leader, chairman Nigel Farage and Jeffrey Titford will divert some of their EU expenses entitlement to a trust fund to finance challenges against the commission. They would also seek to expose fraud and waste, he claimed.

UKIP's three MEPs plan to team up with the anti-EU Independence Europe de Nation grouping set up by the late Sir James Goldsmith.